1. Field of the Invention
The present invention relates to an inductance element and a delay element used for a snubber of a switching power source and a method of manufacturing the same, and a snubber using the same.
2. Description of the Related Art
An inductance element is used in various kinds of electric circuit. For instance, in a switching power source of a ringing choke converter, as a current delay element that delays gate signal of a MOS-FET that is a switching element, an inductance element (saturable inductor) is used. The current delay element makes a snubber condenser function as a resonant condenser to implement zero-voltage switching of the MOS-FET.
As an existing inductance element, one that has a toroidal core formed by winding or stacking for instance a soft magnetic alloy ribbon is mainly used. In applying such an inductance element to the aforementioned current delay element, a plurality of turns of sheathed wire is wound around a toroidal core of closed magnetic circuit structure to obtain prescribed characteristics.
The inductance element having a toroidal core is advantageous in obtaining inductance based on the closed magnetic circuit structure thereof. However, in an toroidal core constituted of a soft magnetic alloy ribbon, different from a sintered core consisting of a ferrite sintered body, a configuration where in advance magnet wire is wound around an insulated bobbin, thereto divided sintered core being butted to constitute a closed magnetic circuit can not be applied with ease.
In order to apply a toroidal core in the aforementioned bobbin structure, similarly with a U-character cut core, a step where the core, after being impregnated with resin, is cut and inserted in the bobbin is necessary. Such processing step not only lowers a manufacturing efficiency of elements to push up the manufacturing cost but also deteriorate magnetic properties due to the cutting of the toroidal core.
From the above, in employing a toroidal core constituted of the existing soft magnetic alloy ribbon, it is general to directly implement the winding to the toroidal core to constitute an inductance element. However, in such a constitution, processing efficiency in implementing the winding to the toroidal core is low, in addition there are difficulties in implementing automation in the winding step. Thereby, the manufacturing cost of the inductance element is pushed up.
In the existing inductance element, in order to reduce number of turns to the toroidal core, for the soft magnetic alloy ribbon, material of high permeability is applied. Thereby, the core of which effective cross-section is increased is used. Even when such a configuration is applied, a problem of inefficiency of the winding can not be cancelled, there fundamentally remains a problem of low productivity.
Further, in a structure where the direct winding is applied to the toroidal core, a core of strength capable of enduring the winding is necessary. Accordingly, resin coating is applied to the toroidal core, or the toroidal core is put in a resin case to use. These steps also cause an increase in the manufacturing cost of the inductance element.
As mentioned above, in the existing inductance element, a structure where the winding is given to a toroidal core consisting of a wound body or a stacked body of a magnetic ribbon is general. A processing efficiency of the winding to the toroidal core is bad and the winding step accompanies difficulties in automating. These cause an increase of the manufacturing cost of the inductance element. Further, to give strength enough to endure the winding operation, the resin coating or resin case is used. These also cause an increase of the manufacturing cost of the inductance element.
Accordingly, an object of the present invention is to provide an inductance element that, while maintaining excellent inductance characteristics, owing to an improvement of processing efficiency of the winding step, enables to drastically lower the manufacturing cost and a method for manufacturing the same. Further, another object of the present invention is, by using such an inductance element, to provide a snubber of which characteristics and productivity are improved.
An inductance element of the present invention comprises a coil provided with winding of which number of turns (N) per unit length of 10 mm is 20 or more and 500 or less, the winding having a hollow portion opened at both ends thereof, and a core having single or a plurality of layers of magnetic ribbon of a thickness of 4 xcexcm or more and 50 xcexcm or less and a width of 2 mm or more and 40 mm or less, at least part of the magnetic ribbon being disposed in the hollow portion, here a ratio (N/n) of the number of turns of the coil (N) to the number of layers of the soft magnetic ribbon (n) being 20 or more and 500 or less.
The inductance element of the present invention is obtained based on the following new knowledge. That is, by forming the winding of a coil in a cylinder opened at both ends thereof one hand, by sufficiently increasing the number of turns on the other hand, even when a cross section of a magnetic ribbon constituting the core is very small, sufficient inductance characteristics can be obtained. Based on such knowledge, in the present invention, a ratio (N/n) of the number of turns of the coil (N) to the number of layers of a magnetic ribbon (n) of a thickness of 4 xcexcm or more and 50 xcexcm or less is set at 20 or more and 500 or less. According to such inductance element, excellent characteristics particularly as a saturable inductor can be obtained.
In the inductance element of the present invention, different from the existing toroidal shape, a winding opened at both ends thereof is applied. Accordingly, compared with the inductance element of the existing toroidal shape, the processing efficiency in the step of winding can be remarkably improved. In specific, the step of coil winding can be easily automated. Thereby, the manufacturing cost of the inductance element can be remarkably lowered. In addition to these, based on the aforementioned N/n ratio, excellent inductance characteristics can be obtained.
As a specific mode of the inductance element of the present invention, a structure can be cited where a cylindrical bobbin having a hollow portion is used, around an external periphery thereof the winding being implemented, a magnetic ribbon being inserted in the hollow portion of the cylindrical bobbin. In an element using such a bobbin, when one end of the hollow portion is closed, the magnetic ribbon can have an open magnetic circuit structure. Further, when the both ends of the hollow portion are opened, by disposing the magnetic ribbon penetrating through the hollow portion thereof and by magnetically connecting the both ends thereof, the magnetic ribbon can have a closed magnetic circuit structure (closed magnetic circuit loop). Thus, the inductance element of the present invention can take various kinds of modes.
Further, another inductance element of the present invention comprises a coil provided with a winding having a hollow portion opened at both ends thereof and a core having single or a plurality of layers of magnetic ribbon of a thickness of 4 xcexcm or more and 50 xcexcm or less, the magnetic ribbon being disposed, so as to form a closed magnetic circuit structure, penetrating the hollow portion, the both ends thereof being magnetically connected.
A method of manufacturing a first inductance element of the present invention comprises the steps of disposing a winding around an external periphery of a bobbin having a hollow portion, disposing a magnetic ribbon in the hollow portion of the bobbin, disposing a lead terminal to the bobbin and electrically connecting an end portion of the winding to the lead terminal, and sealing the hollow portion therein the magnetic ribbon is disposed.
A method of manufacturing a second inductance element of the present invention comprises the steps of disposing a winding to a bobbin having a hollow portion opened at both ends thereof, disposing a magnetic ribbon penetrating in the hollow portion of the bobbin and magnetically connecting both ends of the magnetic ribbon, and disposing a lead terminal to the bobbin and electrically connecting an end of the winding to the lead terminal.
The inductance element of the present invention such as mentioned above has excellent characteristics as a current delay element of a snubber of for instance a switching power source. A snubber of the present invention comprises an inductance element of the present invention like this. In the snubber, an inductance element of the present invention is connected to a driver of a switching element to use.